Conventionally, a data carrier system, which is composed of a data carrier and a reader/writer device to carry out contactless data transmission and reception between the data carrier and the reader/writer device, is practically applied in various fields. In such a data carrier system, an antenna installed in the data carrier receives an alternate magnetic field of carrier frequency supplied from the reader/writer device via an antenna circuit to obtain operating power.
The reader/writer device modulates the magnetic field and transmits an interrogation signal including a command or data, and the data carrier demodulates and receives the command or data transmitted from the reader/writer device.
On the other hand, when transmitting data to the reader/writer device, the data carrier transmits a response by turning on and off a conventional load switch connected to an antenna circuit installed therein, according to the content of the response signal to transmit. In such a structure, a double sideband carrier is used as frequency for responding from the data carrier, with respect to a carrier frequency of the alternate magnetic field supplied from an antenna circuit of the reader/writer device.
The data carrier is composed of a storage unit for storing information and an antenna for transmitting and receiving information in a contactless manner, to transmit and receive information in a contactless manner with the reader/writer device in use of electromagnetic fields or radio waves. Such data carrier is utilized in various fields, being referred to RFID, IC tag, ID tag, RF tag, radio tag, electronic tag, transponder, etc.
As applications of the data carrier system, data carriers are disposed to, for example, vending machines, game machines, electricity meters, gas meters, water meters, home electronics, office automation equipments and productive facilities and information such as operation histories, sales records and used amount is recorded in the storage unit of the data carrier.
The data carrier used in is various fields in various ways. Among those various usage patterns, a data communication device capable of performing both RF communication and contact-type serial communication with a reader/writer device is proposed (for example, see Patent Document 1).
A data communication device described in Patent Document 1 is composed of antenna coil, data communication unit for carrying out contactless data communication with an external communication device via the antenna coil and a data input and output end terminal for transmitting and receiving data to and from the other party, and a contact unit for contacting with the data input and output end terminal. With this structure, serial communication can be carried out via the data input and output end terminal and the contact unit.
The data carrier can be applied in various fields in various ways. A technique for performing communication with a reader/writer device and confirming whether the device component having the data carrier is a previously authenticated device component has been proposed.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2004-214879
[Patent Document 2] Japanese Patent Application Laid-Open No. 2001-134151